Experimental study on shear behavior and shear capacity calculation of coral seawater sea-sand concrete beams reinforced with BFRP-steel composite bars

The use of locally sourced materials from remote offshore island and reef regions can effectively address challenges in island engineering construction, such as shortages of conventional building materials, poor resistance to salt-induced corrosion, and high transportation costs. However, the applicability of conventional structural design methods to such materials remains uncertain. In this study, nine beam specimens were designed and fabricated considering parameters including the presence or absence of web reinforcement, shear span ratio, longitudinal reinforcement ratio, and stirrup spacing. Experimental investigations were conducted on the shear behavior of coral seawater sea-sand concrete (CSSC) beams reinforced with basalt fiber-reinforced polymer (BFRP)-steel composite longitudinal bars and BFRP stirrups. A shear capacity prediction model incorporating the generalized dowel action of longitudinal reinforcement was proposed for such beams, both with and without web reinforcement. The results indicate that providing stirrups significantly enhances the shear capacity of the beams. Depending on the shear span ratio, the failure modes can be classified as diagonal compression failure, shear-compression failure, or diagonal tension failure. The shear capacity increases with decreasing shear span ratio and increasing longitudinal reinforcement ratio, while it decreases with increasing stirrup spacing. Comparisons with existing design codes and relevant research results demonstrate that the proposed calculation method agrees well with the experimental data. These findings provide a useful reference for the structural design of CSSC beams using locally sourced materials in tropical island and reef engineering construction.